The principle of a silver salt diffusion transfer process (hereinafter, referred to as DTR process) is well known as described in, for example, U.S. Pat. No. 2,352,014.
In a DTR process, a silver salt is imagewise transferred from silver halide emulsion layers into an image-receiving layer by diffusion and, in many cases, converted into a silver image in the presence of physical developing nuclei. For this purpose, the silver halide emulsion layer imagewise exposed is disposed in contact with or brought into contact with an image-receiving layer in the presence of a silver halide complexing agent, whereby the unexposed silver halide is converted into a soluble silver complex salt. In the exposed areas of the silver halide emulsion layer, the silver halide is developed (chemical development) into silver and hence silver can no longer dissolve and diffuse. In the unexposed areas of the silver halide emulsion layer, the silver halide is converted into a soluble silver complex salt, which is transferred into the image-receiving layer and usually forms a silver image in the presence of a physical developing nuclei.
In a direct positive silver halide emulsion, the behavior of the silver halide in the exposed areas and the unexposed areas is contrary to the aforesaid case.
The DTR process can be applied in a wide range of fields. Among these fields, in the method of reproducing documents and, in particular, the production of a material for photomechanical process, it is necessary to obtain a silver image having a high density, a high contrast, and a high sharpness in the image-receiving layer. Furthermore, the image reproducing charcteristics, that is, the characteristic of reproducing images from an original as faithful as possible, e.g., reproducing ruled lines having a width of several tens of microns as fine line images as they are is very important. Also, it is particularly important that both the ruled lines of an original having ruled lines (black lines) of a positive image with a white background and ruled lines (white lines) of a negative image with a black background in a disordered state, are faithfully reproduced. In addition, the allowance for the light exposure amount necessary for reproducing these black lines and white lines must be wide (the light exposure latitude is wide), and when a continuous tone original is printed through a contact screen and then a diffusion transfer development is performed, a dot image faithful to the original must be reproduced.
It is well known to form an antihalation layer on a silver halide light-sensitive material (negative working) for obtaining these image reproducing characteristics. When a light-sensitive material is lacking in the antihalation layer, there are defects that fine lines are not reproduced and the exposure latitude is narrowed. Also, in the case of dot images, gradation becomes hard and the reproduction of fine portions is inadequate.
As a pigment which is used in the antihalation layer for improving the image reproducing characteristics, carbon black is usually used.
On the other hand, a typical processing composition which is used for the DTR process contains a silver halide complexing agent such as a thiosulfate, etc., an alkali agent such as sodium hydroxide, etc., a perservative such as a sulfite, etc., and a developing agent such as hydroquinone, 1-phenyl-3-pyrazolidone, etc.
The high-alkaline processing composition containing the developing agent has a disadvantage in that the developing agent losses its effect due to air oxidation. Accordingly, it is known to avoid the foregoing disadvantage by incorporating the developing agent is a light-sensitive material for a DTR process, that is, in a silver halide emulsion layer and/or a hydrophilic colloid layer which is in a water permeable relation with the emulsion layer.
However, even when the developing agent is incorporated in a silver halide emulsion layer or a light-insensitive layer such as a protective layer, an interlayer, a subbing layer, etc., complete avoidance of air oxidation on the developing agent is impossible. As a result, undesirable defects such as reduction of the developing rate, reduction of sensitivity, reduction of silver image density, formation of fog, etc. occur.
The deterioration of the developing agent is caused not only by air oxidation but also by other factors and it has been confirmed that carbon black is one of these factors. The deterioration of the developing agent occurs with almost all hydroquinones, p-aminophenols, ascorbic acid, dihydroxynaphthalenes, etc., and is particularly severe with 1-phenyl-3-pyradolines.
It is well known that carbon black is useful as a pigment for antihalation but it is known that carbon black causes fog when the silver halide light-sensitive material containing it is stored as described in, for example Japanese Patent Application (OPI) No. 68520/75 (corresponding to U.S. Pat. No. 3,900,323). Therefore, the incorporation of carbon black in a silver halide light-sensitive material causes a serious problem in the storage thereof. Further, the incorporation of carbon black in a silver halide light-sensitive material containing a 1-phenyl-3-pyrazolidone causes a more serious problem in the storage thereof.
It is generally considered that the bad influence of carbon black on the formation of fog and on the storage stability of the silver halide light-sensitive material is caused by impurities contained in carbon black. Accordingly, it has keenly be desired to employ other means than carbon black for antihalation.
Dyes are generally considered as antihalation materials in place of carbon black. Dyes for use as antihalation materials for silver halide light-sensitive materials are required to have the properties that they do not diffuse into adjacent layers, they do not dissolve in processing solutions or water, they are incorporated in silver halide light-sensitive materials in high concentration as antihalation materials, and the dye itself or impurities thereof do not give bad influences on the occurence of fog and the storage stability of the light-sensitive materials. However, dyes meeting these requirements have not yet been found. That is, many dyes have such problems that they cannot be incorporated in silver halide light-sensitive materials to an extent of imparting an antihalation effect to the light-sensitive materials in the case of incorporating them in the light-sensitive material by, for example, an oil dispersion or a dispersion with a surface active agent, due to the inferior dispersibility or inferior dissolution, and they diffuse in the adjacent silver halide emulsion layer to desensitize the emulsion layer during coating the silver halide emulsion layers. Further, they are decolored in the coating solution or dissolve in processing solutions or water for washing. In addition, impurities in the dyes adversely influences the desensitization and the storage stability of the light-sensitive materials.